Secretary of State Dean Acheson was focused on containing Communism in Europe. He did pay particular attention to Asia.
The Korean Peninsula had been split at the 38th Parallel following WWII. The Soviet Union controlled the northern portion, while the U.S. controlled the southern portion.
A Communist government was established in the North and a Democratic one was established in the South.
No one expected a Communist attack in the Summer of 1950.
Kim Il Sung was the leader of North Korea. He was a dictator . He held absolute power in North Korea. He desired to unite Korea as one, Communist government.
Syngman Rhee was the leader of South Korea. He was a nationalist and hated Communism. He was backed by the United States.
Mr. Rhee also wanted to unite Korea, but under a democratic government.
North Korea invaded South Korea in June of 1950. It was a surprise attack that caught South Korea and the United States by surprise.
The United States responded by sending supplies and eventually troops to aid the South Korean Army.
With help from the U,S., the Communist forces were expelled from South Korea.
China then entered the war to come to the aid of North Korea. This completely surprised the United States, again. Eventually, the war became a stalemate . A truce was finally signed in the middle of 1953.